The present invention concerns formed materials mainly for personal care products like diapers, training pants, swim wear, absorbent underpants, adult incontinence products and feminine hygiene products. This material may also be useful for other applications such as, for example, in bandages and wound dressings, nursing pads and in veterinary and mortuary applications.
Personal care articles usually have multiple layers of material of some sort to absorb liquids from the body. These layers may include natural fibers, synthetic fibers and superabsorbent particles in varying proportions. When liquid such as urine is deposited into a personal care product like a diaper, it goes through the uppermost layers, typically a liner against the body and a xe2x80x9csurgexe2x80x9d or xe2x80x9cintakexe2x80x9d layer designed to provide temporary liquid holding capacity. The product may also have a xe2x80x9cdistributionxe2x80x9d layer designed to move liquid in the X and Y directions in order to utilize more of the absorbent core. After going through these upper layers, the urine enters the absorbent core portion of the product. The absorbent core permanently retains the liquid.
Various approaches have been used in the past to hold liquid, yet still allow it to be transferred eventually to another layer like the core. Similarly, intake materials have been investigated which take in liquid with varying degrees of success. There remains a need in the art for a fabric for use in personal care products with improved fluid handling capabilities. Such a material will intake and retain fluid more efficiently than has been practiced in the past.
In response to the discussed difficulties and problems encountered in the prior art, a new structural composite comprising a nonwoven fabric made of a homogeneous blend of large and small denier synthetic fibers has been developed. The nonwoven material is for personal care products and is made from a mixture of fibers of different denier, where a first denier fiber has an average denier at least 3 denier less than a second fiber and the second fiber has an average denier between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. The first denier fiber has an average denier of 2 or less and the second denier fiber preferably has an average denier between 6 and 15.
The nonwoven material can have the first denier fiber present in an amount between 25 and 75 weight percent and the second denier fiber present in an amount between 75 and 25 weight percent. More particularly the first denier fiber can be present in an amount between 40 and 60 weight percent and the second denier fiber can be present in an amount between 60 and 40 weight percent. Still more particularly, the first denier fiber can be present in an amount of about 60 weight percent and the second denier fiber can be present in an amount of about 40 weight percent.
The first denier fiber may be a bicomponent fiber and may be a sheath/core bicomponent fiber selected of the group consisting of polyethylene/polypropylene, polyethylene/polyethylene terephalate and co-polyethylene terephalatel polyethylene terephalate bicomponent fibers. The second denier fiber may be made from a polyester. The fibers may have a hydrophilic treatment added to their surface.
The material made from the homogeneous blend of mixed denier fibers may be used as a surge material in personal care products. When used as a surge material in personal care products the material is capable of taking in fluid at a rate of 12 to 20 cc/sec. When used as a surge material in conjunction with a standard liner the structure is capable of up to an 8, 15 or even 20 percent TEWL improvement, when compared to a large fiber denier surge using the same standard liner.
Particular embodiments include a surge material for personal care products having between 40 and 60 weight percent of a first fiber having a first average denier and between 60 and 40 weight percent of a second fiber having a second average denier, where the first average denier is at least 3 denier less than the second average denier, the second average denier is between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. Another embodiment is one in which the surge material for personal care products has about 60 weight percent of a first fiber in a bicomponent sheath/core configuration, made from polymers selected of the group consisting of polyethylene/polypropylene, polyethylenelpolyethylene terephalate and co-polyethylene terephalate/polyethylene terephalate and having a first average denier, and about 40 weight percent of a polyester second fiber having a second average denier, where the first average denier is at least 3 denier less than the second average denier, the second average denier is between 4 and 15, and where the material has a basis weight between 30 and 200 gsm. The small or first fiber has a average denier less than the large average denier fiber and the large or second denier fiber has a average denier between 4 and 15.
These materials are suitable for use in personal care products like diapers, training pants, incontinence products, bandages, and sanitary napkins.
As used herein the term xe2x80x9cnonwoven fabric or webxe2x80x9d means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
xe2x80x9cHydrophilicxe2x80x9d describes fibers or the surfaces of fibers that are wetted by the aqueous liquids in contact with the fibers. The degree of wetting of the materials can, in turn, be described in terms of the contact angles and the surface tensions of the liquids and materials involved. Equipment and techniques suitable for measuring the wettability of particular fiber materials can be provided by a Cahn SFA-222 Surface Force Analyzer System, or a substantially equivalent system. When measured with this system, fibers having contact angles less than 90xc2x0 are designated xe2x80x9cwettablexe2x80x9d or hydrophilic, while fibers having contact angles equal to or greater than to 90xc2x0 are designated xe2x80x9cnonwettablexe2x80x9d or hydrophobic.
xe2x80x9cSpunbonded fibersxe2x80x9d refers to small diameter fibers that are formed by extruding molten thermoplastic material as filaments from a plurality of fine capillaries of a spinneret. Such a process is disclosed in, for example, U.S. Pat. No. 4,340,563 to Appel et al. and U.S. Pat. No. 3,802,817 to Matsuki et al. The fibers may also have shapes such as those described, for example, in U.S. Pat. No. 5,277,976 to Hogle et al. which describes fibers with unconventional shapes.
xe2x80x9cBonded carded webxe2x80x9d refers to webs that are made from staple fibers which are sent through a combing or carding unit, which separates or breaks apart and aligns the staple fibers in the machine direction to form a generally machine direction-oriented fibrous nonwoven web. This material may be bonded together by methods that include point bonding, through air bonding, ultrasonic bonding, adhesive bonding, etc.
xe2x80x9cAirlayingxe2x80x9d is a well-known process by which a fibrous nonwoven layer can be formed. In the airlaying process, bundles of small fibers having typical lengths ranging from about 3 to about 52 millimeters (mm) are separated and entrained in an air supply and then deposited onto a forming screen, usually with the assistance of a vacuum supply. The randomly deposited fibers then are bonded to one another using, for example, hot air to activate a binder component or a latex adhesive. Airlaying is taught in, for example, U.S. Pat. No. 4,640,810 to Laursen et al., and U.S. Pat. No. 5,885,516 to Christensen.
As used herein xe2x80x9cthermal point bondingxe2x80x9d involves passing a fabric or web of fibers to be bonded between a heated calender roll and an anvil roll. The calender roll is usually, though not always, patterned in some way so that the entire fabric is not bonded across its entire surface, and the anvil roll is usually flat. As a result, various patterns for calender rolls have been developed for functional as well as aesthetic reasons. One example of a pattern has points and is the Hansen Pennings or xe2x80x9cHandPxe2x80x9d pattern with about a 30% bond area with about 200 bonds/square inch as taught in U.S. Pat. No. 3,855,046 to Hansen and Pennings. The HandP pattern has square point or pin bonding areas wherein each pin has a side dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches (1.778 mm) between pins, and a depth of bonding of 0.023 inches (0.584 mm). The resulting pattern has a bonded area of about 29.5%. Another typical point bonding pattern is the expanded Hansen Pennings or xe2x80x9cEHPxe2x80x9d bond pattern which produces a 15% bond area with a square pin having a side dimension of 0.037 inches (0.94 mm), a pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches (0.991 mm). Another typical point bonding pattern designated xe2x80x9c714xe2x80x9d has square pin bonding areas wherein each pin has a side dimension of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins, and a depth of bonding of 0.033 inches (0.838 mm). The resulting pattern has a bonded area of about 15%. Yet another common pattern is the C-Star pattern which has a bond area of about 16.9%. The C-Star pattern has a cross-directional bar or xe2x80x9ccorduroyxe2x80x9d design interrupted by shooting stars. Other common patterns include a diamond pattern with repeating and slightly offset diamonds with about a 16% bond area and a wire weave pattern looking as the name suggests, e.g. like a window screen, with about a 19% bond area. Typically, the percent bonding area varies from around 10% to around 30% of the area of the fabric laminate web. As is well known in the art, the spot bonding holds the laminate layers together as well as imparts integrity to each individual layer by bonding filaments and/or fibers within each layer.
As used herein, through-air bonding or xe2x80x9cTABxe2x80x9d means a process of bonding a nonwoven bicomponent fiber web in which hot air is forced through the web. The temperature of the air is sufficient to melt one of the polymers of which the fibers are made. The air velocity is usually between 100 and 500 feet per minute and the dwell time may be as long as 6 seconds. The melting and resolidification of the polymer provides bonding. Through-air bonding (TAB) requires the melting of at least one component to accomplish bonding, so it is usually restricted to webs with two components like conjugate fibers or those which include an adhesive. In the through-air bonder, air having a temperature above the melting temperature of one component and below the melting temperature of another component is directed from a surrounding hood, through the web, and into a perforated drum supporting the web. Alternatively, the through-air bonder may be a flat arrangement wherein the air is directed vertically downward onto the web. The operating conditions of the two configurations are similar, the primary difference being the geometry of the web during bonding. The hot air melts the lower melting polymer component and thereby forms bonds between the filaments to integrate the web.
xe2x80x9cPersonal care productxe2x80x9d means diapers, training pants, swim wear, absorbent underpants, adult incontinence products, bandages and feminine hygiene products. It further encompasses veterinary and mortuary products.
Basis Weight: A circular sample of 3 inches (7.6 cm) diameter is cut and weighed using a balance. Weight is recorded in grams. The weight is divided by the sample area. Five samples are measured and averaged.
Material caliper (thickness): The caliper of a material is a measure of thickness and is measured at 0.05 psi (3.5 g/cm2) with a STARRET(copyright) bulk tester, in units of millimeters. Samples are cut into 4 inch by 4 inch (10.2 cm by 10.2 cm) squares and five samples are tested and the results averaged.
Density: The density of the materials is calculated by dividing the weight per unit area of a sample in grams per square meter (gsm) by the material caliper in millimeters (mm). The caliper should be measured at 0.05 psi (3.5 g/cm2) as mentioned above. The result is multiplied by 0.001 to convert the value to grams per cubic centimeter (g/cc). A total of five samples would be evaluated and averaged for the density values.
FIFE: The horizontal Fluid Intake and Flowback Evaluation (FIFE) was performed on all samples to determine the intake potential of the composites. The FIFE entails insulting the structure by pouring a defined amount of 0.9 percent saline solution into a cylindrical column resting vertically on top of the structure and recording the time it takes for the fluid to be taken in by the structure. The sample to be tested is placed on a flat surface and the FIFE testing apparatus placed on top of the sample. The FIFE testing apparatus consisted of a rectangular, 35.43 by 20.3 cm, plexiglas flat piece upon which was centered a cylinder with an inside diameter of 30 mm. The flat piece had a 38 mm hole corresponding with the cylinder so that fluid could pass through it from the cylinder to the sample. The FIFE testing apparatus weighed 0.52 kg (1.14 pounds).
Intake times are typically recorded in seconds. Samples were cut into 2.5 by 7 inch (6.35 by 17.8 cm) pledgets and were inserted into a HUGGIES(copyright) step 4 diaper as a surge. The samples were then insulted three times at 100 mL per insult with a wait of 15 minutes between the time the fluid was completely absorbed and the next insult.
After the third insult, the materials were placed on a vacuum box under 0.5 psi of pressure with a piece of blotter paper on top. The blotter paper was 110 lb. Verigood paper made by Fort James Corporation and was 3.5 by 12 inches (8.9 by 30.5 cm). The blotter paper was weighed before and after the test and the resulting differential reported as the flowback value as grams of fluid desorbed.
Permeability: Permeability is obtained from a measurement of the resistance by the material to the flow of liquid. A liquid of known viscosity is forced through the material of a given thickness at a constant flow rate and the resistance to flow, measured as a pressure drop is monitored. Darcy""s Law is used to determine permeability as follows:
Permeability=[flow ratexc3x97thicknessxc3x97viscosity/pressure drop]xe2x80x83xe2x80x83[Equation 1]
where the units are:
The apparatus consists of an arrangement wherein a piston within a cylinder pushes liquid through the sample to be measured. The sample is clamped between two aluminum cylinders with the cylinders oriented vertically. Both cylinders have an outside diameter of 3.5 inches (8.9 cm), an inside diameter of 2.5 inches (6.35 cm) and a length of about 6 inches (15.2 cm). The 3 inch diameter web sample is held in place by its outer edges and hence is completely contained within the apparatus. The bottom cylinder has a piston that is capable of moving vertically within the cylinder at a constant velocity and is connected to a pressure transducer that is capable of monitoring the pressure encountered by a column of liquid supported by the piston. The transducer is positioned to travel with the piston such that there is no additional pressure measured until the liquid column contacts the sample and is pushed through it. At this point, the additional pressure measured is due to the resistance of the material to liquid flow through it. The piston is moved by a slide assembly that is driven by a stepper motor. The test starts by moving the piston at a constant velocity until the liquid is pushed through the sample. The piston is then halted and the baseline pressure is noted. This corrects for sample buoyancy effects. The movement is then resumed for a time adequate to measure the new pressure. The difference between the two pressures is the pressure due to the resistance of the material to liquid flow and is the pressure drop used in Equation (1). The velocity of the piston is the flow rate. Any liquid whose viscosity is known can be used, although a liquid that wets the material is preferred since this ensures that saturated flow is achieved. The measurements were carried out using a piston velocity of 20 cm/min, mineral oil (Peneteck Technical Mineral Oil manufactured by Penreco of Los Angeles, Calif.) of a viscosity of 6 centipoise.
TransEpidermal Water Loss (TEWL):
Skin hydration values are determined by measuring TransEpidermal Water Loss (TEWL) and can be determined by employing the following test procedure.
The test is conducted on adults on the forearm. Any medications should be reviewed to ensure they have no effect on test results and the subject""s forearms should be free of any skin conditions such as rashes or abrasions. Subjects should relax in the test environment, which should be at about 72xc2x0 F. (22xc2x0 C.) with a humidity of about 40 percent, for about 15 minutes prior to testing and movement should be kept to a minimum during testing. Subjects should wear short sleeve shirts, not bathe or shower for about 2 hours before testing, and should not apply any perfumes, lotions, powders, etc., to the forearm.
The measurements are taken with an evaporimeter, such as a DERMALAB(copyright) instrument distributed by Cortex Technology, Textilvaenget 1 9560 Hadsund Denmark.
A baseline reading should be taken on the subject""s forearm and should be less than 10 g/m2/hr. Each test measurement is taken over a period of two minutes with TEWL values taken once per second (a total of 120 TEWL values). The digital output from the Evaporimeter EP1 instrument gives the rate of evaporative water loss (TEWL) in g/m2/hr.
The end of a dispensing tube is placed on the mid-forearm for carrying out the test. is The eye of the tube should be facing the target loading zone. A product to be tested is placed on the subject""s forearm directly over the end of the tube. The product may vary depending upon the type of material to be tested or material availability so care should be taken to ensure that test results are comparable. A stretchable net such as that available from Zens Industrial Knit Products of Milwaukee, Wis., should be placed over the product to help to hold it in place.
Three equal loadings of 70 ml of physiologic saline available from VWR Scientific Products (800-932-5000) at about 95xc2x0 F. (35xc2x0 C.) are delivered to the product at an interval of 45 seconds at a rate of 300 mils/minute by a pump such as a MASTERFLEX(copyright) Digi-Static batch/dispense pump. After 60 minutes, the product is removed from the subject""s forearm and Evaporimeter readings taken immediately on the skin where the product had been.
TransEpidermal Water Loss values are reported as the difference between the one hour and baseline values in g/m2/hr.
Horizontal Wicking: This test measures how far liquid will move in a fabric when only one end of the fabric is immersed in the liquid and the fabric is horizontal. The fabric to be tested is prepared by cutting it into 1 inch (2.5 cm) by 8 inch (20.3 cm) strips in the machine direction. The sample is weighed and marked every 0.5 inch (13 mm) in the long dimension. The sample is placed on a 5 inch (12.7 cm) by 10 inch (25.4 cm) horizontal wire grid and slightly weighted so that it remains flat on the wire. A half inch of one end of the sample is submerged in a 0.5 inch deep by 0.5 inch wide by 5 inch long reservoir containing 10 ml of dyed 8.5 g/l saline solution. The end of the sample in the reservoir is held in place with a cylindrical glass stirring rod having a length of 1.5 inches (3.8 cm) and a diameter of {fraction (5/16)} inches (7.9 mm) which also is submerged in the saline solution. The sample is allowed to rest with one end submerged in the reservoir for 20 minutes and is then carefully pulled horizontally out of the reservoir, cut at each 0.5 inch mark and each section weighed.
The dry sample weight is subtracted from the wet sample weight to arrive at fluid grams, and the 0.5 inch submerged in the reservoir is not considered. The total distance wicked is recorded along with the total grams of fluid wicked.